Re: Help inserting many-to-many (more info)

I rearranged the code a bit to see the results. I saved changes to the 
story and then tried adding the relationship to the categories,

//get the ec, insert story (EOGeneric) into it, save changes
EOEditingContext	ec = session().defaultEditingContext();
ec.insertObject(story);
story.takeValueForKey(((Session)session()).getUserId(), "userId");
story.takeValueForKey(new NSTimestamp(), "datePosted");
ec.saveChanges();

ec.invalidateObjectsWithGlobalIDs(new 
NSArray(ec.globalIDForObject(story)));

//for each category, add the story to both sides of the relationship
Enumeration		ite = selectedCategories.objectEnumerator();
while (ite.hasMoreElements())
{
	Category cat = (Category)ite.nextElement();
	cat.addObjectToBothSidesOfRelationshipWithKey(story, "stories");
}
ec.saveChanges();

This gives me a different-yet-still-baffling exception at the second 
saveChanges(), I'm hoping some will be able to shed some light on this 
:P Or can anyone share a snippet of a many-to-many snippet that works?

java.lang.NullPointerException
<snip>.EODatabaseContext._verifyNoChangesToReadonlyEntity
<snip>.EODatabaseContext.performChanges
<snip>.EOObjectStoreCoordinator.saveChangesInEditingContext
<snip>.EOEditingContext.saveChanges